Assays for Actin Sliding Movement over Myosin-Coated Surfaces

One important result from in vitro studies of the interaction of the major proteins of muscle, actin and myosin, has been the growing recognition that nearly any aspect of muscle mechanics can be studied in a model system consisting of purified proteins. This chapter is a compilation of techniques for purified in vitro motility assays for actin sliding movement over myosin. Several forms of myosin, including filaments, monomers, and soluble proteolytic fragments, have been found to work well in aetin sliding movement assays. The focus is limited to studies using skeletal muscle proteins, but only slight modification of these protocols may be necessary for proteins derived from smooth muscle and nonmuscle sources. The properties of the protein preparations used are critical to reproducibility of actin sliding movement assays. The methods presented in the chapter are trustworthy preparations but are not singularly successful. However, in particular it should be noted that myosin subfragment preparations that work well in solution experiments might not be optimal for use in movement assays.